Heating systems for buildings are well known in the art. Traditionally, such systems have consisted of step heating systems. For step heating systems, a plurality of step heating elements, for example heating coils, are installed in series, generally in an air circulation duct or other means of directing air flow. Typically, a sufficient total quantity N of heating coils is installed to meet the heating needs of a discrete heated space, for example 1 or more rooms, of a building. Each step heating element is connected to a corresponding step heating mechanical relay which closes and opens to, respectively, enable and disable a circuit providing power to the heating element to activate and deactivate the circuit. Typically, there is one corresponding mechanical relay for each step heating element. Thus, for a total quantity N of step heating elements, there is an equal total quantity N mechanical relays. All of the mechanical relays are connected, directly or indirectly, to a step heating controller which provides signals thereto to activate and deactivate the relays based on input received from a sensor, for example a heat sensor, thermometer, or air flow sensor disposed in the heated space or air flow duct connecting thereto. The relays, and therefore step heating elements, are sequentially activated and deactivated in predefined ascending and descending sequence or series, i.e. such that a heating element and second corresponding relay connected thereto are not activated until a first eating element and corresponding relay connected thereto are activated. Similarly, a third heating element and corresponding relay and are not activated until the first and second corresponding relays and heating elements are activated. In the same fashion, a second heating element and corresponding relay connected thereto is not deactivated unless the third heating element and corresponding relay is already deactivated. Thus, for total quantity N heaters (or steps), the heaters are switched on as required based on the heat detected by the sensor, in sequential order, providing increasing proportional heating, until a desired level of temperature is detected by the heat sensor, as follows: 0/N, 1/N, 2/N, . . . R/N, where R is less than or equal to N and represents a required quantity of heating elements to generate a required amount of heat to achieve the desired level of temperature, with R=N corresponding to all step heating elements being activated and the maximum amount of heating being provided. The relays and step heaters are deactivated by the step heating controller in exactly the reverse order. Each sensor and controller may also connected to a main heating controller responsible for controlling the heating for many heated spaces, for example rooms, hallways, or the like within a building. Typically, it is the main heating controller and/or the controller which determines the quantity of heating elements to activate and deactivate as described above.
Unfortunately, such traditional step heating systems are quite costly in that they require, for each step heating element, an accompanying mechanical relay. Further, such step heating systems can be quite unreliable, since if a mechanical relay fails, then the heating element connected thereto will also become unavailable. Further, the lifetime of the mechanical relays, due to the mechanical nature thereof, is relatively short, typically about 0.1 megacycles of switching or 100,000 cycles of activation or deactivation. Thus, both inconveniently and expensively, the relays have to be replaced relatively often.
More recently, to circumvent the aforementioned disadvantages associated with step heating systems, pulse modulation heating systems were developed. For such systems, there are H, typically one, pulse heating elements per heated space, again placed in the path of air flow such as an adjoining air circulation duct or system. The maximum heating capacity of the H pulse heating elements for the pulse modulation system is approximately equal, over a predefined heating cycle C, to that which would be provided by the quantity of N step heating elements, when all N step heating elements are activated, in a step heating system for the same heated space over the duration of the heating cycle C. The heating cycle C may be defined in terms of a maximum number of electronic pulses MP for a predefined period of time T, for example 120 pulses over one or more units of time, or simply as a predefined period of time T in conventional units of time, such as seconds or minutes. Once again, a heat sensor for the heated space detects the temperature therein and is connected to a pulse heating controller connected to the H pulse heating elements and which activates and deactivates the pulse heating elements. The pulse heating controller and sensor may also, as in a step heating system, be connected to a main heating controller.
Instead of using mechanical relays for sequentially turning on and off the pulse heating elements, the pulse heating controller of the pulse modulation system has a solid state relay, connected directly to all of the H pulse heating elements. The pulse heating controller activates the H pulse heating elements by sending signals thereto through the solid state relay as, or during, a quantity P of electronic pulses emitted during the time period T of heating cycle C, with the quantity of pulses PP sent being equal to or less than the predefined maximum quantity of pulses MP defined for the time period T of the heating cycle. Thus, based on the input from the heat sensor, the pulse heating controller activates the solid state relay and pulse heating element connected thereto, for a variable quantity PP of pulses, out of the maximum quantity MP possible, for the period of time T of the heating cycle C, based on the amount of heating required. Thus, if more heating is required, the variable quantity P of pulses is increased, wherein if less or no heating is required, the variable quantity PP is reduced. Typically, zero-crossing switches or relays are used for the pulse modulation system, with the solid state relay being actuable (ON) and deactuable (OFF) for activating and deactivating the relay and pulse heating element at about 0 volts AC crossing of the AC signal, the AC signal preferably being about 60 Hz.
Advantageously, compared to heat stepping systems, the pulse modulation systems can be implemented with only one pulse heating element per discrete heating space of each building, which reduces material, maintenance, and installation costs, as well as installation and maintenance time. Further, for pulse modulation heating systems, there is typically only one solid state relay per heated space, which further reduces costs. Additionally, the solid state relay, which has a lifespan between 10 and 100 million cycles, is far more durable than mechanical relays used by step heating systems, further reducing maintenance costs.
Given the above advantages of pulse modulation systems compared to step heating systems, replacement of step heating systems with pulse modulation heating systems is highly desirable. However, since the step heating controllers and main heating controller controllers, common in many older buildings, for step heating systems are configured to sequentially activate and deactivate a plurality of mechanical relays and pulse heating elements, based on heating needs, as opposed to activating a single solid state relay for a fixed portion of time or pulses, i.e. P, of a total heating cycle interval of time or pulses, i.e. T, replacement of a step heating system may require, even for a single heated space, replacement of the main system for an entire building, not to mention the relays and step heating controllers.
Accordingly, there is a need for an improved pulse modulation heating system and method.